Process for the preparation of dicyanoacetylene



United States Patent Ofifice 3,070,622 Patented Dec. 25, 1962 r 3,070,622 PROCESS FOR THE PREPARATEON F DHCYANGMCETYLENE Elmore L. Martin, Wilmington, Del assfgnor to E. 1. du Pont de Nernours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Aug. 30, 1961, Ser. No. 134,819 11 Claims. (Cl. 260-4658) This invention relates to the preparation of dicyanoacetylene.

Dicyanoacetylene is a member of a class of organic nitrogen compounds known as cyanocarbons, which have recently become of special interest because of their unusual chemical properties. Dicyanoacetylene is an active dienophile and undergoes addition reactions with halogens, hydrogen halides, alcohols and amines. It is notably useful as a high temperature fuel which is capable of burning with flame temperatures of 5200 to 6100 K. in controlled combustion with oxygen or ozone. The only method heretofore known for the preparation of dicyanoacetylene gives quite variable yields in a tedious process for dehydration of acetylenedicarboxamide by means of phosphoric anhydride.

It has now been discovered that dicyanoacetylene can be prepared by pyrolysis of l,Z-dichloro-1,2-dicyanoethylene or by simultaneous pyrolysis of 1,2-dich1oro-1,2- dicyanoethylene and 1-choro-1,Z-dicyanoethylene. The pyrolysis of 1,Z-dichloro-1,2-dicyanoethylene is illustrated by the following equation:

01 01 NCC=(ilON NCOECON+ C12 In this process either the trans or the cis 1,2-dichloro- 1,2-dicyanoethylene, or a mixture of them in any proportion, can be used. These isomeric compounds are ordinarily known as dichlorofumaronitrile (trans) and dichloromaleonitrile (cis), respectively. Likewise, the cis (monochloromaleonitrile) and/ or tran (monochlorofurnaronitrile) form of l-chloro-l,Z-dicyanoethylene may be used in admixture with the 1,Z-dichloro-l,Z-dicyanoethylene. Preferably, 1,2dichloro-1,2-dicyanoethylene is the only reactant.

Pyrolysis is carried out at temperatures in the range or" 300 to 750 C., preferably 400 to 690 C. The reaction is conveniently accomplished at atmospheric pressure, but the pressure is not critical and can be below or above atmospheric pressure. The purity of the 1,2-dichloro-1,2-dicyanoethylene, alone or in admixture with l-chloro-l,2-dicyanoethylene, is not critical provided, of course, that the impurities do not eifect substantially deleterious side reactions. For example, the presence or absence of moisture is not critical in the process, but it is preferable to maintain substantially anhydrous conditions to avoid possible loss of dicyanoacetylene by adventitious hydrolysis or hydration.

A diluent is not necessary, but can be used if desired. For convenience, the 1,2-dichloro-l,2-dicyanoethylene, alone or in admixture with the 1-chloro-1,2-dicyanoethylone, can be dissolved in an inert solvent such as benzene and the solution pumped or injected into the reactor. Although it is not essential, an inert carrier gas such as helium or nitrogen can be used to transport the nitriles, alone. or in solution in benzene, into the pyrolysis zone and to conduct th pyrolysate into a fractionating apparatus or into cooled condensing receivers. When an inert carrier gas is used, the amount is not critical, but it is usually employed in proportionately large volume with respect to the vaporized dichloro and/ or monochloro compounds. Preferably, the inert carrier gas represents about 0.02-0.20%, by volume, of the feed stream.

The crude pyrolysate can be separated into purified product and unchanged starting material by ordinary fractional distillation; by a gas-liquid partition process, e.g., gas chromatography; or by fractional condensation, e.g., in a series of traps at successively lower temperatures.

In the preparation of dicyanoacetylene by the process of the invention, reaction time, i.e., residence time at reaction temperature, is not critical and can be varied from a fraction of a second to many minutes. However, at subpyrolysis temperatures, chlorine can re-add to the acetylenic product; and therefore, it is preferable to remove chlorine promptly, and this can be accomplished by various means; for example, by use of a chlorine scavenger such as a reactive metal or a paraffin hydrocarbon (e.g., the method of US. 2,447,410), or by arrangement in the pyrolysis apparatus for physical separation of chlorine from other products. Physical separation can be accomplished by conducting the vaporized pyrolysate in an inert carrier gas directly from the pyrolysis Zone into a receiver kept at a temperature below about 0 C. and above about 35 C., whereby dicyanoacetylene and unchanged 1,2 dichloro-1,2-dicyanoethylene and/ or 1-chloro-1,2-dicyanoethylene are retained in the receiver in the form of a nonvolatile condensate while uncondensed chlorine is transported away by the carrier gas.

Although the material of which the pyrolysis apparatus is constructed is not critical, it is advantageous to use a material that does not melt at the pyrolysis temperature, and is resistant to attack by chlorine. Suitable construction materials include quartz, copper, nickel, stainless steel, copper-nickel alloy, or nickel-iron-molybdenum alloy. Glass can be used in the lower part of the temperature range.

The invention is illustrated in greater detail in the fol lowing, examples.

EXAMPLES I-IV General Procedure In these examples, pyrolyses of 1,2-dichloro-1,2-dicyanoethylene were carried out in a conventional pyrolysis apparatus having a pre-heater section and a pyrolyser sec-' tion packed with to 200 mesh quartz chips. The pyrolyser section was connected directly to a conventional gas chromatographic analytical set-up which was equipped to collect eluted fractions if desired. I

In the pyrolyses, helium was employed as a carrier gas and the vaporized 1,2-dichloro-l,Ldicyanoethylene carried amounted to about 0.020.05%, by volume, of the gaseous feed stream. The preheat temperature was 216 C., and in each run the 1,2-dichloro-1,2-dicyanoethylene, in liquid form as a melt or as a solution in benzene, was introduced into the preheated helium stream in a single injection. The total pyrolysate passed immediately into the gas chromatographic analyser, which Was calibrated for analysis of mixtures containing chlorine, benzene, dichlorofumaronitrile, dichloromaleonitrile and dicyanoacetylene. For this calibration, authentic dicyanoacetylene was prepared by phosphoric anhydride dehydration of acetylenedicarboxamide according to the method of Moureau and Bongrand, Ann. chim. [9] 14, 546- (1920). In one run the gas chromatographic analysis was-checked qualitatively, by collecting the dicyanoacetylene eluent in a trap cooled in liquid nitrogen and verifying the identity of the trapped product by infrared spectrographic analysis [cf. Miller and Hannan, J. Chem; Phys. 21, 11 0 Experimental Data Data for specific pyrolyses of 1,2-dichloro-1,Z-dicyanoethylene are presented in Table I. For clarity in this table, the pyrolysate data show only dicyanoacetylene, dichlorofumaronitrile and dichloromaleonitrile in proportions adjusted to 100% total based on the gas chromatographic analyses, which, of course, also contain data, not shown, on chlorine and solvent components of the total gen was the carrier gas reveal that the use of nitrogen is more practical than the use of helium.

' products. Dicyanoacetylene is useful as a high temperature fuel TABLE I [Abbreviations D EN dlchlorofumaronitriie; D CMN =dich1oromaleonitrile; D CA dicyanoacetylene] Pyrolysate Starting Reaction Contact Example Solvent Material Temp., (time/ 0. sec.) Percent Percent Percent DOA DCFN DCMN I-A BeWene.-. DCFN 435 7.4 19. 3 47.0 33.7 DGMN l 435 7.4 10.1 46.1 43.8 DCFN 535 6.5 14. 4 45. 8 39. 8 DCMN 1 535 6. 5 8. 6 49. 5 41.9 DCFN 615 5.9 42. 3 35. 5 22. 2 DCMN l 615 5.9 18.8 55.3 25.9 1 DCFN/ 730 0.1 Present 1 DCMN 1 The concentration of DCFN or DCMN in 1 Contact time, i.e., residence time benzene is by weight. of reactant in the pyrolyser, is based on flow rate of 1,2-dicyanoethylene being considered of negligible proportions.

In the foregoing examples both dichlorofumaronitrile and dichloromaleonitrile are shown to be present in the pyrolysate, whether or not one or the other was absent at the start. These data testify to the occurrence of thermal cis-trans isomerization of l,2-dichl0ro-1,2-dicyanoethylene in the temperature range of the process.

The 1,Z-dichloro-1,2-dicyanoethylene used in the process illustrated by the foregoing examples is readily prepared by chlorination of succinonitrile according to the method of US. 2,443,494. In the succinonitrile chlorination product, there is often present a substantial amount of monochlorofumaronitrile and occasionally lesser amounts of monochloromaleonitrile that can be converted to l,2-dichl0ro-1,2-dicyanoethylene, if desired, by further chlorination. However, for the purpose of preparing dicyanoacetylene by the process of this invention, it is unnecessary to remove l-chloro-l,2-dicyanoethylene from the crude succinonitrile chlorination product, since the monochloro compound does not interfere with the pyrolytic dechlorination of the dichloro compounds and is, itself, a source of dicyanoacetylene through dehydrochlorination. The process of preparing dicyanoacetvlene by pyrolysis of 1,Z-dichloro-l,2-dicyan0ethylene that contains a substantial amount of l-chloro-l,2-dicyanoethylene is illustrated by the following example.

EXAMPLE V A mixture of the distillate obtained from chlorination of succinonitrile, containing 17.7% monochlorofumaronitrile, 53.2% dichlorofumaronitrile, and 29% dichloromaleonitrile, was pyrolysed at 550 C. by the procedure of Examples I-IV, but without the use of benzene as an inert solvent. The analyser showed the presence of 8.3% chlorine, 7.9% hydrogen chloride, 30% dicyanoacetylene, 29.3% dichlorofumaronitrile, and 29% dichloromaleonitrile in the pyrolysate. Assuming complete conversion of monochlorofumaronitrile, dicyanoacetylene attributable to dechlorination of the 1,2-dichloro-1,2-dicyanoethylenes was obtained in 31% conversion and 69% yield. This result demonstrates the utility of crude 1,2- dichloro-l,2-dicyanoethylene, prepared by chlorination of succinonitrile, as a raw material in the pyrolytic preparation of dicyanoacetylene.

It is to be understood that, although a carrier gas was employed in Examples I-V, its use is not essential. Also, experiments similar to Example V in which nitro because it has a high endothermic heat of formation, and because in controlled combustion it produces highly stable carbon monoxide and nitrogen [cf. Kirschenbaum and v. Grosse, I. Am. Chem. Soc. 78, 2020 (1956)]. It is also useful in the preparation of chemical derivatives; for example, by reaction with cyclopentadiene it forms a 1:] adduct which is useful as an insecticide for control of silk worm or Colorado potato beetle [cf. Blomquist and Winslow, J. Org. Chem. 10, 149 (1945)].

Since obvious modifications and equivalents in the invention will be evident to those skilled in the chemical arts, I propose to be bound solely by the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

I claim:

1. The process of preparing dicyanoacetylene which comprises pyrolysing l,2-dichloro-1,Z-dicyanoethylene at a temperature of 300-750 C.

2. The process of claim 1 wherein 1,2-dichloro-1,2-dicyanoethylene is in admixture with 1-chloro-1,2-dicyanoethylene.

3. The process of claim 1 wherein the temperature is 40069() C. and the pressure is atmospheric.

4. The process of claim 1 wherein the 1,2-dichloro- 1,2-dicyanoethylene is dissolved in an inert solvent.

5. The process of claim 4 wherein the solvent is benzene.

6. The process of claim 1 wherein the 1,2-dichloro- 1,2-dicyanoethylene is conducted into the zone of pyrolysis by an inert carrier gas.

7. The process of claim gas is helium.

8. The process of claim 6 wherein the inert carrier gas is nitrogen.

9. The process of claim 1 wherein the 1,2-dichloro-1,2- dicyanoethylene is dissolved in an inert solvent and is conducted into the zone of pyrolysis by an inert carrier gas.

10. The process of claim 9 wherein said solvent is benzene and said carrier gas is helium.

11. The process of claim 1 wherein the pyrolysis is conducted in the presence of a chlorine scavenger.

6 wherein the inert carrier No references cited. 

1. THE PROCESS OF PREPARING DICYANOACETYLENE WHICH COMPRISES PYROLYSING 1,2-DICHLORO-1,2-DICYNOETHYLENE AT A TEMPERATURE OF 300-750*C. 